1 88 THE CRUSTACEA 



of inshore waters. In Arctic seas the Cumacea are conspicuous by 

 their abundance and relatively large size, but they are also common 

 in suitable localities in tropical waters. Many species, often also 

 of considerable size, occur in the deep sea. 



The thirteen species known from the Caspian Sea all belong 

 to the family Pseudocumidae, and were originally referred to the 

 single genus Pseudocuma, which comprises only three truly marine 

 species. It is interesting to note that several of the Caspian 

 species " mimic " in their general aspect widely different genera of 

 other families, and have on this account received such specific 

 names as diastyloides, eudorelloides, and campylaspoides. 



The largest known Cumacean is the Arctic Diastylis Goodsiri 

 (Fig. Ill), which reaches a length of 35 mm. Some deep-sea 

 species are not much inferior to this, but the average size is much 

 less, and some species do not exceed 1*5 mm. in length. 



No fossil Cumacea are known. 



AFFINITIES AND CLASSIFICATION. 



The systematic position of the Cumacea has been somewhat 

 obscured by the customary classification of the Malacostraca into 

 Edriophthalma and Podophthalma, since they unite the sessile eyes 

 of the former group with the carapace of the latter. As a matter 

 of fact, apart from characters of specialisation which seem to have 

 arisen within the order, they clearly stand midway between the 

 Mysidacea and the Tanaidacea, just as they combine, to some 

 extent, the swimming powers of the one with the burrowing habits 

 of the other. 



ORDER Cumacea, Kroyer (1846). 



Family BODOTRIIDAE. Bodotria, Goodsir (= Cuma, H. Milne- 

 Edwards) ; Cyclaspis, G. 0. Sars ; Zygosiphon, Caiman. Family VAUN- 

 TOMPSONIIDAE. Vauntompsonia, Spence Bate. Family LEUCONIDAE. 

 Leucon, Kroyer ; Eudorella, Norman. Family NANNASTACIDAE. Nan- 

 nastacus, Spence Bate ; Campylaspis, G. 0. Sars ; Platycuma, Caiman. 

 Family CERATOCUMIDAE. Ceratocuma, Caiman. Family PSEUDOGUMIDAE. 

 Pseudocuma, G. O. Sars ; Pterocuma, G. O. Sars (Fig. 1 1 3). Family 

 LAMPROPIDAE. Lamprops, G. 0. Sars ; Pamlamprops, G. 0. Sars. Family 

 PLATYASPIDAE. Platyaspis, G. O. Sars. Family DIASTYLIDAE. Diastylis, 

 Say (Fig. Ill); Diastyloides, G O. Sars. 



LITERATURE. 



1. Caiman, W. T. On the Cumacea. Rep. Pearl Fisheries Ceylon. Roy. Soc. 



ii. pp. 159-180, 5 pis., 1904. 



2. The Marine Fauna of the West Coast of Ireland : Part IV. Cumacea. 



Fisheries, Ireland, Sci. Invest., 1S04, i. 52 pp. 5 pis., 1905. 



